Except they totally are writing crypto related code. It's called SecureRandom for a reason. If I as a user of Ruby see that code I have certain expectations regarding that. If the Ruby coder maintaining that code is not capable of doing the work required to satisfy those expectations then as I said there is much more wrong than just this bug.

It's reasonable to make this mistake initially sure. But when it's pointed out to you that the documentation is flat out wrong for reasons outside your and others control and you are pointed at articles and research by the experts in this field and you elect to ignore them then the security flaws that will result are very much on you just as much as they are on the linux man page maintainer.